1. Field of the Invention
The present invention relates to an electrostatic actuator and a driving method thereof, particularly, to an electrostatic actuator of a small power consumption and a driving method thereof.
2. Description of the Related Art
An electrostatic actuator in which a movable section is vertically driven by the electrostatic force is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 2001-346385, Japanese Patent Disclosure No. 2002-199747, Japanese Patent Disclosure No. 2003-9550 and Japanese Patent Disclosure No. 2003-164167. As disclosed in these patent documents, the electrostatic actuator is constructed such that a movable section equipped with a movable electrode is arranged between a pair of stator electrodes, and the movable section is vibrated in the vertical direction by controlling the voltage applied to the stator electrodes and the movable electrode. Also, at least one of the stator electrodes is formed of a plurality of segment electrodes that are electrically separated. In the construction in which the segment electrodes are arranged in the moving direction of the movable section, the movable section can be moved slightly by sequentially shifting the voltage applied to the segment electrodes. To be more specific, in the electrostatic actuator comprising a plurality of segment electrodes, the movable section is displaced forward or backward while being vibrated in the vertical direction when the movable section is directed toward the segment electrodes. Therefore, the movable section is moved forward or backward depending on the shift direction of the voltage applied to the segment electrodes.
The electrostatic actuator can be miniaturized by fine processing so as to make it possible to move slightly the movable section and, thus, is said to be utilized in various fields. For example, where an electrostatic actuator is mounted to a photographing apparatus such that a photographing lens is mounted to the movable section, it is possible to form a lens system capable of zooming. Also, in the electrostatic actuator that is simply vibrated in the vertical direction, it is possible to mount a photographing CCD to the movable section such that the movable section is moved in the vertical direction in accordance with the external vibration so as to realize a mechanism for counteracting the effect of hand vibration in a camera apparatus.
The electrostatic actuator itself has a low power consumption and the movable section can be driven with a low power consumption. In this electrostatic actuator, it is necessary for the movable section to be attached to one of the stator sections in order to prevent the movable section from being operated. To be more specific, the movable section itself is slightly movable between a pair of stator sections. Therefore, if the stator electrode and the movable electrode are connected to the ground potential during the holding mode in which the apparatus is under the inoperative state, the movable section is moved between the stator sections by the external force or by the own weight, with the result that it is possible for the movable section to be brought into contact inadvertently with the stator section so as to break the movable section or the stator electrode. In order to prevent the movable section from being moved freely under the inoperative state, a voltage is applied between the movable section and one of the stator electrodes so as to permit the movable section to be kept attached to the stator electrode and, thus, the movable section is made immovable. Even under the inoperative state, a voltage is required to be applied intermittently between the movable section and the one of the stator electrodes. What should be noted is that, even if the electrostatic actuator can be driven with small power consumption in the driving stage, a problem arises that the power is consumed in the inoperative stage, though the power consumption is small. It follows that the conventional electrostatic actuator is substantially incapable of realizing a driving apparatus of a small power consumption so as to give rise to the problem that the battery life of the miniaturized apparatus is shortened.